Cut the top and the bottom off of each zucchini and allow them to cool. Once cooled, cut them into large chunks.
Combine zucchini, tahini, lemon juice, garlic cloves, and olive oil in blender or food processor and blend until smooth. Transfer to a bowl and drizzle additional olive oil over the top, if desired. (I also like sprinkling mine with a little smoked paprika. It's not traditional, but it's delicious!) Serve with fresh veggies, pita bread or chips, or crackers.
To grill the zucchini, lightly oil the outside and place them directly on the grates of your grill. The cook time depends on the type of grill you have and how hot it is, so it's hard to be precise. Just keep an eye on the zucchini and turn them every so often. You don't want them to burn, but they should have nice grill marks on them.